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Effectiveness of increased salt iodine concentration on iodine status: trend analysis of cross-sectional national studies in Switzerland

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Abstract

Purpose

Despite longstanding voluntary salt iodisation in Switzerland, data suggest inadequate iodine intake in vulnerable population groups. In response, the salt iodine concentration was increased from 20 to 25 mg/kg and we assessed the impact on iodine status.

Methods

We conducted a cross-sectional national study in school-age children (n = 731), women of reproductive age (n = 353) and pregnant women (n = 363). We measured urinary iodine concentration (UIC) and urinary sodium concentration (UNaC) in spot urine samples. The current median UIC was compared with national data from 1999, 2004 and 2009. We measured TSH, total T4 and thyroglobulin (Tg) on dried blood spot samples collected in women.

Results

The median UIC (bootstrapped 95% CI) was 137 µg/L (131, 143 µg/L) in school children, 88 µg/L (72, 103 µg/L) in women of reproductive age and 140 µg/L (124, 159 µg/L) in pregnant women. Compared to 2009, the median UIC increased modestly in school children (P < 0.001), but did not significantly change in pregnant women (P = 0.417). Estimated sodium intake exceeded the recommendations in all population groups. The prevalence of thyroid disorders in women was low, but Tg was elevated in 13% of the pregnant women.

Conclusion

Iodine intake is overall adequate in Swiss school-age children, but only borderline sufficient in pregnant and non-pregnant women, despite high salt intakes and satisfactory household coverage with iodized salt. Our findings suggest increasing the concentration of iodine in salt may not improve iodine intakes in women if iodised salt is not widely used in processed foods.

Registration

This trial was registered at clinicaltrials.gov as NCT02312466.

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Abbreviations

DBS:

Dried blood spot

EAR:

Estimated average requirement

Tg:

Thyroglobulin

TSH:

Thyroid stimulating hormone

TT4:

Total thyroxine

UCC:

Urinary creatinine concentration

UIC:

Urinary iodine concentration

UIE:

Urinary iodine excretion

UNaC:

Urinary sodium concentration

UL:

Upper level

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Acknowledgements

The study was funded by the Federal Food Safety and Veterinary Office (FSVO), Bern, Switzerland, and ETH Zurich, Zurich, Switzerland. We would like to thank the subjects for their participation and, teachers, doctors and nurses for assistance with subject recruitment and sample collection. We thank ETH students Leonie Arns, Friederike Becker, Matthias Buchli, Simon Hartung, Lisa Mazzolini, Laura Salvioni, Elisabeth Schlunke, Sara Stinca, Alexandra Thoma and Lea Wildeisen for assistance with the study and support with laboratory analysis. We also thank Leonie Arns for conducting the statistical analysis of the prevalence of inadequate iodine intake and Stefan Trachsel for providing salt sales data from the Swiss Saltworks AG.

Author information

The author’s responsibilities were as follows—MA, IHA, MBZ: designed the research and wrote the study protocol; MA, IHA: supervised the study; SH: assisted with study coordination and conducted biochemical analysis of TSH, TT4 and Tg; RF: supervised the measurement of TSH and TT4; MA: conducted the statistical analysis and wrote the paper. MA had primary responsibility for final content. All authors read, edited, and approved the final version of the manuscript.

Correspondence to Maria Andersson PhD.

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Andersson, M., Hunziker, S., Fingerhut, R. et al. Effectiveness of increased salt iodine concentration on iodine status: trend analysis of cross-sectional national studies in Switzerland. Eur J Nutr (2019). https://doi.org/10.1007/s00394-019-01927-4

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Keywords

  • Iodine
  • Iodine deficiency
  • Urinary iodine concentration
  • Salt iodisation
  • Switzerland